This invention relates to apparatus for supplying gas for unclogging the openings through which fluidising gas is supplied to a fuidisation bed.
The apparatus is useful with fluidisation grids which have openings for the fluidisation air which are likely to become blocked by falling solid particles.
The invention can be used with the fluidisation grids referred to as "fluidisation plates", which are grids having in their thickness funnel-shaped cavities in the upper part, for example inverted truncated pyramids or truncated cones to which fluidisation gas supply tubes are connected.
In order to obtain a satisfactory operation of a fluidized bed, it is important that the following two conditions are met: a suitable distribution, generally an equal distribution, of the flidisation gas through the openings of the grid is obtained; after each stoppage in fluidisation, the solid particles are put back into fluidisation and the grid openings are cleared, so that after the stoppage the restart of fluidisation of the bed can be carried out without obstruction of the individual fluidisation air tubes. This operation is referred to herein as unclogging.
Apparatus which offers a solution for unclogging is described in FR-A-2,171,945. This French patent specification describes apparatus in which the openings for blowing are supplied by individual tubes, which each contain a valve for adjusting the flow rate, a stop valve, a diaphragm and a means for arresting the particles, consisting of a syphon. If particles have accumulated in each syphon when the speed of the fluidisation gas has become insufficient or zero, they are driven off with compressed air, the stop valve then being shut, and fluidisation air is then supplied to the openings for blowing once again.
This device is effective, but it is complex and expensive, because as many valves, diaphragms and syphons have to be installed as there are openings in the grid.
Sometimes, the means for arresting particles which fall consists of at least one elbow formed by a horizontal part and a vertical part of each tube. Other constructional arrangements may be used to provide means for arresting the fall of particles during stoppages in operation.
An unclogging device which does not comprise a valve, a diaphragm or a syphon on each individual tube, but has a semipermeable component placed in the cross-section of each of the tubes which supply the blow openings of the grid is described in French patent application No. 85/08320, filed on July 3, 1985. This device is often satisfactory because it is simpler and more economical to install then the previous one. However, it could involve a greater head loss and increase correspondingly the energy requirement for blowing the fluidisation gas.